1. Field of the Invention
The present invention relates to a method of facilitating the approach to a platform by an aircraft, and in particular a short landing aircraft, such as an aircraft provided with a rotary wing, for example.
The invention is thus situated in the technical field of systems for providing assistance in piloting an aircraft, and in particular automated systems for providing rotorcraft with assistance in approaching installations at sea.
2. Description of Related Art
Such an installation at sea is provided with a landing zone on which an aircraft is able to land. Thus, the installation at sea may be a mobile platform, a fixed platform, a ship, or even a barge.
For convenience, an installation of this type is referred to below as a “platform”.
A rotary wing aircraft must be able to find and approach platforms safely, regardless of weather conditions and visibility, and while avoiding any obstacles present in the approach area.
The approach is conducted while taking into account: the direction and the speed of the wind in the sector; the type of platform being approached (stationary or mobile platforms, ships, or barges); obstacles in the vicinity (cranes, barges, ships used for positioning the platform, container or super tanker type ships navigating near the approach area, or other platforms in the vicinity); and the comfort of passengers.
Platform approaches are generally made up of the following flight segments.
Thus, the approach comprises an arrival segment that connects the last flight point of the flight stage in progress to an initial approach point referred to as the initial approach fix (IAF). The arrival segment is sometimes positioned at an altitude of 1500 feet (ft). It should be recalled that one foot (ft) is equivalent to 30.48 centimeters (cm).
An initial approach segment may connect the initial approach fix IAF to a final approach point referred to as the final approach fix (FAF). The purpose of this segment is to align the aircraft, to decelerate, and to prepare for the final approach segment.
At least one final approach segment connects the final approach fix FAF to a decision point referred to as a missed approach point (MAP).
If a pilot establishes visual contact with the platform at the decision point, the pilot may land the aircraft on that platform.
However, if visual contact with the platform is not obtained at this point in the approach, it is necessary to follow a segment referred to as the go-around segment. The go-around segment may also be followed at any moment in the approach if the crew judges that to be useful. The aim of this go-around segment is to reach a safe altitude.
During adverse weather conditions, an instrument approach is likely to stress the crew, who must pilot the aircraft manually in order to guide it towards a zone in which visual acquisition of the platform can be obtained.
During the transition between the instrument flight stage and the visual flight stage, the crew must constantly be switching between what is displayed on the piloting screens of the instrument panel and what is observed outside in order to detect any sign/visual indication making it possible to confirm the position of the platform (lights, portions in relief). This manner of approaching a platform is therefore not the most practical and may sometimes create errors in interpretation, for example in the presence of fog causing visual acquisition of the landing target to be lost temporarily.
Instrument approaches to a platform or a moving vessel are generally performed without using a navigation computer, referred to as a Flight Management System (FMS), and without the aircraft autopilot being coupled with an approach path predefined by the Flight Management System.
At present, certain platforms are fitted with a device, referred to as a “Non Directional Beacon” (NDB), that is used by the crew via the navigation computer as means for assisting navigation and for correlating the position of the aircraft with relative accuracy, but these means do not enable an approach flight plan to be constructed.
A navigation computer is known that is used to provide horizontal guidance during the en route stage, where the en route stage corresponds to the stage of flight being followed before the approach flight stage. For the approach flight stage, and as means for providing assistance in navigation, the crew determines an off-route target point corresponding to the coordinates of the platform to be reached. However, the navigation computer does not segment the various stages of the approach towards the platform in order to servo-control the autopilot on the guidance data (horizontal or vertical deviation, speed setpoint).
The approach is thus performed manually or semi-automatically with the assistance of certain advanced modes of the autopilot by using the approach charts published by operators and approved by local authorities.
Furthermore, the weather radar of the aircraft may be used as means for identifying the platform and for detecting and avoiding temporary or permanent obstacles during the approach and the final descent.
Document US 2010/0168939 proposes a module and an automated method of approaching a platform on an approach path constructed from approach points.
In that document US 2010/0168939, a pilot inputs into a module of the aircraft:
the coordinates of the target platform to be reached; a final approach course towards the platform;
an offset distance extending laterally between the path to be followed by a path directed towards the platform following that approach heading; and
a descent height.
Under such circumstances, the aircraft module determines in particular the position of the initial approach fix IAF and of the final approach fix FAF in response to the data as input. The aircraft is thus directed towards the initial approach fix IAF.
Thus, the constructed approach path includes a horizontal segment connecting an initial approach fix IAF to a final approach fix FAF.
Then, the path has a descent segment and a leveling-off segment in order to connect the final approach fix FAF to a decision point MAP.
The initial approach fix IAF, the final approach fix FAF, and the decision point MAP are contained in a vertical plane parallel to the selected approach course. It should be understood that “vertical plane” refers to a plane extending in the gravity direction, points of said vertical plane being located at various altitudes.
The vertical plane is offset relative to the platform by a distance equal to the input offset distance.
Thus, that document does not take specific features of platforms into consideration. But platforms are of various shapes. The position of a platform landing zone may thus be far away from the coordinates of the platform that were input.
The technological background also includes the following documents:
Esterline CMC electronics, CMA-9000 flight management system operator's manual, operational program S/W 169-614876-022, publication No 9000-GEN-0105, itel N). 930-6000088-00, Aug. 21, 2008;
N. McFarlane, A new procedure for North Sea Helicopter Operations, Second GIANT use forum, Brussels, Belgium, Oct. 9, 2008;
“EGNOS Offshore Helicopter Approach Procedure”, GIANT GNSS INTRODUCTION IN THE AVIATOR SECTOR, Jan. 24, 2008, XP003032932;
K. M. Dodson and J. R. A. Stevens, A North Sea trial to investigate the use of Differential GPS for instrument Approaches to Offshore Platforms, paper presented at the 23rd European Rotorcraft Forum, Dresden, Germany, September 1997; and
Advisory circular AC 90-80Bn of Dec. 4, 1999.